<!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        /* 
            min-width表示大于多少像素时生效
            max-width表示小于多少像素时生效
         */
         /* 宽大于700像素，小于1200像素时生效 */
        @media screen and (min-width:700px) and (max-width:1200px){
            body{
                background-color:#bfa;
            }
        }
    </style>
</head>
<body>

</body>
</html>